Liquid crystal display device and manufacturing method thereof

ABSTRACT

A liquid crystal display device superior in mass productivity and improved image quality with a higher contrast ratio by decreasing the occurrence of defective display due to the disorder of the initial liquid crystal alignment and realizing stable alignment of liquid crystals, comprising: a pair of substrates  101  and  102 , at least one of which is transparent; a liquid crystal layer  110 ′ disposed between the pair of substrates; a group of electrodes formed on at least one of the pair of substrates to apply an electric field to the liquid crystal layer; plural active elements  115  connected to the group of electrodes; and an orientation control film  109  disposed on at least one of the pair of substrates, wherein said orientation control film made of a photosensitive polyimide, a polyamide acid ester and a polyamide acid is given orientation control ability by being irradiated with substantially linearly polarized light.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photo-alignment-method-applied liquidcrystal display device and its manufacturing method.

2. Description of the Related Art

Commonly, display by a liquid crystal display device is implemented byapplying voltage to liquid crystal molecules in a liquid crystal layersandwiched between a pair of substrates so as to change the orientationof liquid crystal molecules and by utilizing the resultant change in theoptical properties of the liquid crystal layer. Liquid crystal displaydevices provided with a switching device such as a thin film transistoron a pixel-by-pixel basis, which are commonly referred to asactive-drive-type liquid crystal display devices, are conventionallyrepresented by the Twisted Nematic (TN) display type. This type haselectrodes formed on each of the two substrates forming a pairsandwiching the liquid crystal layer such that voltage is applied to theliquid crystal layer substantially perpendicularly to the boundary facesbetween the substrates and the liquid crystal layer and implementsdisplay by utilizing the optical rotatory effect of liquid crystalmolecules constituting the liquid crystal layer. The largest problemwith liquid crystal display devices of this TN type is their narrowviewing angles.

Also known is the IPS type which has inter-digital electrodes formed onone of a pair of substrates so that an electric field substantially inparallel with the surfaces of the substrates is generated to implementdisplay by utilizing the birefringence of the liquid crystal layer, thatis, by rotating liquid crystal molecules constituting the liquid crystallayer in a plane substantially parallel with the substrates. Due to thein-plane switching of liquid crystal molecules, this IPS type has awider viewing angle, lower load capacitance and other advantages overthe TN type. Considered promising as a new liquid crystal display devicewhich may replace the TN type, the IPS type is recently making rapidprogress. Disclosed in Patent JP-A-9-73101 is an IPS type which attainedimproved transmittance by using a transparent conductive film to formone or both of a pair of electrodes to apply an electric field to theliquid crystal layer.

Due to superior viewing angle characteristics (luminance contrast ratioand tone/color inversion) and bright display, the IPS type liquidcrystal display device (hereinafter, denoted as “IPS-TFT-LCD”) is apromising technology for monitors and televisions having wider displayareas. In the IPS-TFT-LCD, orientation control films given thecapability to control the orientation of liquid crystals are formed onthe respective interfaces of the liquid crystal layer with the pair ofsubstrates which sandwich the liquid crystal layer. In this connection,however, it is still difficult to practically manufacture 20-inch orlarger size IPS-TFT-LCDs (large panels) unless a new structure orprocess is developed.

In the case of the IPS-TFT-LCD, it is especially difficult to impartuniform alignment treatment to the whole area of the large orientationcontrol films because of many steps in contact with the liquid crystallayer. As compared with the conventional TN type and in particular withthe currently-popular normally-open TN type (bright with low voltage anddark with high voltage), the margin allowed for the alignment treatmentof the orientation control films is remarkably narrow. This narrowmargin is attributable to the following three points (1) to (3).

(1) Stepped Structure

Due to the principle, the IPS-TFT-LCD is required to have a number ofabout-several-μm-wide, long, thin electrodes (sometimes referred to asinter digital electrodes) disposed therein. Therefore, fine stepstructures are formed. Although dependent on the thicknesses of theelectrodes and the geometries of various films formed thereon, theirheights usually exceed 10 nm. In a high-transmissivity pixel structure,a thick inorganic insulating film is formed, and its surface has acertain level of planarity regardless of the surface irregularities ofthe layers below it. Thus, in the high-transmissivity pixel structure,the steps (surface irregularities) of the orientation control film aremainly attributable to the top electrode layer. Over these steps, anorientation control film (also referred to as an alignment film) made ofpolyimide or other polymer is formed.

In the conventional mass-production technology, a rubbing process isperformed on this orientation control film in order to impart a liquidcrystal alignment (initial alignment) ability to the film. The rubbingcloth comprises 10-to-30-μm diameter, thin fibers bound together.Substantially, the liquid crystal alignment ability is imparted to thealignment film as a result of each fine fiber giving a certaindirectional shearing force locally to the film. Although very thinfibers in the order of several microns are available, such very thinfibers are not practically used for the rubbing alignment since rigidityis needed to give a certain level of frictional force. In the IPSscheme, since the inter-electrode space ranges approximately from 4 to30 μm and therefore is substantially the same as or smaller than thefiber diameter, poor alignment is likely to occur around the steps dueto insufficient rubbing. This poor alignment results in lower imagequality since it lowers the black level (blackness) and consequentlylowers the contrast ratio and lowers the luminance uniformity.

(2) Alignment Angle

Due to the principle, the IPS-TFT-LCD is required to set the initialalignment direction deviated from the longitudinal direction ofelectrodes or from the direction perpendicular to that longitudinaldirection by a certain angle. Here, the electrodes refer to signal lineelectrodes, common electrodes within pixels, and pixel electrodes. Todefine the initial alignment direction by rubbing, it is necessary torub the alignment film with 10-to-30-μm fibers in a direction inclinedat a predetermined angle as described above. However, fibers tend to bedragged along the edges of steps formed due to wiring lines extending ina particular direction, such as signal line electrodes, commonelectrodes within pixels, and pixel electrodes. This disturbs thealignment, resulting in a shallower black level and other disadvantagesin image quality.

(3) Deepening of Black Level

One of the characteristics of the IPS-TFT-LCD is its superior indeepening the dark level (black display). Accordingly, disorder in thealignment is likely to be visually noticeable as compared with othertypes. In the conventional normally-open TN type, a dark level isattained when high voltage is applied. In this case of the high voltage,almost all liquid crystal molecules are oriented in the direction of theelectric field perpendicular to the substrates. The dark level isobtained by the relationship between the alignment of the liquid crystalmolecules at high voltage and the arrangement of polarizers. Thus,theoretically, the dark level uniformity is not much subject to theinitial state of orientation at low voltage. Further, human eye aresensitive to changes of the black level since they perceive luminanceunevenness as a relative ratio of luminance and its perception reactssubstantially on a logarithmic scale. In this respect, the conventionalnormally-open TN type has an advantage since liquid crystal moleculesare forcibly oriented to one direction with high voltage irrespective ofthe initial state of orientation.

In the case of the IPS type, since the dark level display is produced atlow or zero voltage, the IPS type is sensitive to the disorder of theinitial orientation. In particular, if liquid crystal molecules arehomogeneously oriented such that they are parallel to the upper andlower substrates and if polarizers are arranged such that the opticaltransmission axis of one polarizer is parallel to the orientationdirection of the liquid crystal molecules and that of the otherpolarizer is orthogonal to that orientation direction of the liquidcrystal molecules (called birefringence mode), polarized light incidenton the liquid crystal layer travels without being linearly disturbedalmost at all. This is effective in deepening the dark level.

In the birefringence mode, transmittance T is commonly given by thefollowing equation.T=T ₀·sin^(2{)2θ(E)}·sin²{(π·deff·Δn)/λ}

In the equation, T₀ is a coefficient determined mainly by thetransmittances of the polarizers used in the liquid crystal panel; θ(E)is the angle between the orientation direction of liquid crystals(effective optical axis of the liquid crystal layer) and thetransmission axis of polarized light; E is the intensity of an appliedelectric field; deff is the effective thickness of the liquid crystallayer; Δn is the anisotropic refractive index of the liquid crystals;and λ is the wavelength of the light. The product of the effectivethickness of the liquid crystal layer, deff, and the liquid-crystalanisotropic refractive index Δn, i.e., deff·Δn, is called retardation.Note that the liquid crystal layer's effective thickness deff is not thewhole thickness of the liquid crystal layer but the partial thickness ofthe liquid crystal layer where the orientation directions of the liquidcrystal molecules actually change when voltage is applied. This isbecause liquid crystal molecules near the boundary faces of the liquidcrystal layer do not change their orientation direction due to anchoringeffects near the boundary faces even when voltage is applied. Thus, thewhole thickness dLC of the liquid crystal layer sandwiched by thesubstrates is always larger than deff, i.e., deff<dLC. This differencecan be roughly estimated to be from 20 nm to 40 nm although dependent onwhat substances respectively constitute the liquid crystal layer and thealignment films in contact with the liquid crystal layer.

As is obvious from the above equation, only the term sin^(2{)2θ(E)} ofthe equation is dependent on the electric field intensity. The luminancecan be adjusted by changing the angle θ according to the electric fieldintensity E. Operation of the normally-closed type is sensitive to thedisorder of the initial alignment since the polarizers are arranged suchthat θ is 0 degrees when voltage is not applied.

Thus, uniform alignment is very important for the IPS type. Accordingly,problems of the conventional rubbing method have come to the fore.Generally, the rubbing alignment has many problems with its rubbingprocess, including not only damage to TFTs by frictionally chargedelectricity and defective display due to poor alignment attributable tothe disordered fiber ends of the rubbing cloth and dust but also thenecessity to frequently replace the rubbing cloth. In order to solvethese problems of the rubbing alignment process, various methods capableof imparting the liquid crystal aligning properties without rubbing,which are commonly referred to as “rubbing-less” alignment methods, havebeen studied and proposed. Among them is the photo-alignment techniquewhich irradiates a polymer film with polarized ultraviolet light or thelike to give the film the ability to align liquid crystal moleculeswithout conducting the rubbing process.

An example of this technique is disclosed in Gibbons et al., “Nature,”Vol. 351, p. 49 (1991). Not needing the conventional rubbing process,this technique can impart the liquid crystal aligning ability to a filmby irradiating it with polarized light. Unlike the rubbing method, thisphoto-alignment method is free from film surface damage, staticelectricity and other problems. In addition, its simplicity as amanufacturing process is advantageous in terms of industrialmanufacturing. Accordingly, this method is gathering attraction as a newmethod for giving the liquid crystal aligning ability without performingthe rubbing process.

As the material for the liquid crystal alignment film, it is proposed touse a polymer compound having a photoreactive group introduced to sidechains thereof since the material must be photochemically sensitive topolarized light. Polyvinyl cinnamate may be cited as a major example. Inthis case, dimerization at the side chains caused by irradiation isthought to produce anisotropy in the polymer film, thereby aligningliquid crystals. It is also proposed to distribute alow-molecular-weight dichroic azo dye in the polymer material andirradiate the film surface with polarized light to create the liquidcrystal aligning ability in the film. Further, it is reported that aspecific polyimide, if irradiated with polarized ultraviolet light orthe like, aligns liquid crystal molecules. The liquid crystal aligningability in this case is considered attributable to depolymerization ofpolyimide main chains in a fixed direction by irradiated light.

SUMMARY OF THE INVENTION

As above, the optical-irradiation photo alignment is proposed anddiscussed as a rubbingless alignment method to solve the problems of therubbing alignment method. To put this method to practical use, however,the following problems have yet to be solved. In the case of polyvinylcinnamate and other polymer materials which have photosensitive groupsintroduced to side chains thereof, reliability is not enough forpractical use since the thermal stability of alignment is notsatisfactory. Structurally, it is thought that the liquid crystalaligning ability is created locally at the polymer side chains in thiscase. This may be not preferable in aligning liquid crystals moreuniformly and strongly. Distribution of a low-molecular-weight dichroicdye among polymer molecules is also not satisfactory in thermal andoptical reliability in view of practical application since the liquidcrystal alignment dye itself is low in molecular weight.

Further, the method of irradiating a specific polyimide with polarizedultraviolet light cannot easily secure sufficient reliability inpractical application since the alignment mechanism is considered to beattributable to photo-induced depolymerization although the polyimideitself is highly reliable in thermal stability. That is, unless theliquid crystal alignment ability attained by irradiating with polarizedlight is improved in stability or durability, these photo-alignmentmethods cannot be used practically. Temporal liquid crystal alignmentability is not satisfactory. In view of practical industrialapplication, it is also desirable to select a thermally stable polymerstructure. In these respects, the polymer materials proposed so far foroptical-irradiation alignment are not necessarily sufficient to attainstrong and stable orientation control of liquid crystals, posing thelargest problem in the way of realizing the optical-irradiationrubbingless alignment.

Recently, demand for more stable alignment is further intensifying.Polyimide photo-alignment films, made from thermally treated polyamideacids, are becoming incapable of meeting the required level. Extensivestudies by the present inventors have revealed that polyimidephoto-alignment films attained by thermally imidating polyamide acidsare low in molecular weight since drastic thermal depolymerizationoccurs during the thermal process. This reduction in molecular weightdue to the thermal treatment lowers the stability of liquid crystalorientation, causing image persistence (image burn-in) in a liquidcrystal display device.

The IPS-TFT-LCD has an inherent problem that the manufacturing marginallowed for the alignment process is narrower as mentioned earlier. Itis thus an object of the present invention to provide a liquid crystaldisplay device, in particular, a large scale one, capable of displayinghigher-contrast-ratio and higher-definition images, by solving the aboveproblem and consequently reducing defective display due to the variationof the initial orientation direction and realizing stable liquid crystalorientation. It is another object of the present invention to provide amanufacturing method superior in mass productivity forhigh-image-quality and high-definition liquid crystal display devices.

The present invention provides a liquid crystal display devicecomprising: a pair of substrates, at least one of which is transparent;a liquid crystal layer disposed between the pair of substrates; a groupof electrodes formed on at least one of the pair of substrates to applyan electric field to the liquid crystal layer; plural active elementsconnected to the group of electrodes; and an orientation control filmdisposed on at least one of the pair of substrates, wherein at least oneof the orientation control film is made of photosensitive polyimide andpolyamide acid ester and is given orientation control ability by beingirradiated with almost linearly polarized light.

Use of the polyamide acid ester material according to the presentinvention can reduce thermal depolymerization during thermal treatment.It is therefore possible to improve the stability of liquid crystalorientation in a liquid crystal display device where photo-alignment isapplied.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross-section of a pixel in Embodiment 1 for explaininghow one pixel is constructed.

FIGS. 2A, 2B, and 2C depict a top view and cross-sections of the pixelfor explaining how one pixel is constructed in Embodiment 1.

FIG. 3 depicts a cross-section of a pixel in Embodiment 2 for explaininghow one pixel is constructed.

FIGS. 4A, 4B, and 4C depict a top view and cross-sections of the pixelfor explaining how one pixel is constructed in Embodiment 2.

FIG. 5 depicts a cross-section of a pixel in Embodiment 3 for explaininghow one pixel is constructed.

FIG. 6 depicts a cross-section of a pixel in Embodiment 4 for explaininghow one pixel is constructed.

FIG. 7 depicts a cross-section of a pixel in Embodiment 5 for explaininghow one pixel is constructed.

FIG. 8 depicts a top view of the pixel for explaining how one pixel isconstructed in Embodiment 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An orientation control film according to the present invention containspolymer units of a polyamide acid amide represented by the followinggeneral formula (102) or (103), a polyamide acid alkyl silyl esterrepresented by the following general formula (113) or (114), and/or apolyamide acid ester represented by the following general formula (116)or (117). In the formulae, each R1 is individually hydrogen or an alkylgroup containing 1 to 8 carbon atoms, each R2 is individually a hydrogenatom, fluorine atom, chlorine atom, bromine atom, phenyl group, alkylgroup containing 1 to 6 carbon atoms, alkoxy group containing 1 to 6carbon atoms, vinyl group (—(CH₂)m-CH═CH₂, m=0, 1, 2) or alkynyl group(—(CH₂)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound.

The above-mentioned structure enables reduction of thermaldepolymerization during thermal treatment. This structure improves thestability of liquid crystal orientation and can very effectivelysuppress image persistence (burn-in) in liquid crystal display devices.

The above-mentioned orientation control film according to the presentinvention may contain a polyamide acid represented by the followinggeneral formula (121) or (122). In the formulae, each R2 is individuallya hydrogen atom, fluorine atom, chlorine atom, bromine atom, phenylgroup, alkyl group containing 1 to 6 carbon atoms, alkoxy groupcontaining 1 to 6 carbon atoms, vinyl group (—(CH₂)m-CH═CH₂, m=0, 1, 2)or alkynyl group (—(CH₂)m-C≡CH, m=0, 1, 2), and Ar is an aromaticcompound.

Since the above-mentioned polyamide acid is contained, it is possible toreduce the resistivity of the alignment film and therefore veryeffectively suppress image persistence (burn-in) in liquid crystaldisplay devices.

According to the present invention, the above-mentioned aromaticcompound Ar contains at least one of those represented by the followinggeneral formulae (1) through (11).

Individually, each hydrogen molecule of the aromatic rings may insteadbe a fluorine atom, chlorine atom, bromine atom, phenyl group, alkylgroup containing 1 to 8 carbon atoms, alkoxy group, vinyl group oralkynyl group. X is any of an alkyl group containing 1 to 8 carbonatoms, alkoxy group, vinyl group or alkynyl group or an alkyl groupcontaining 0 to 8 carbon atoms and the following functional group, (—O—,—CO—, —COO—, —S—, —SO—, —SO₂—, —NH—, —N═N—, phenyl group). Y is anaromatic ring such as a phenyl group, naphthyl group, anthracene group,or pyrene group wherein each hydrogen atom of the aromatic ringsindividually may instead be a fluorine atom, chlorine atom, bromineatom, phenyl group, alkyl group containing 1 to 8 carbon atoms, alkoxygroup, vinyl group, or alkynyl group. Z is any of the followingfunctional groups, (—CH₂—, —CO₂—, —NH—, —O—, —S—, —SO—, —SO₂—) whereineach hydrogen atom may instead be a fluorine atom, chlorine atom,bromine atom, phenyl group, alkyl group containing 1 to 8 carbon atoms,alkoxy group, vinyl group or alkynyl group.

Specifically, the compounds represented by general formulae (7) through(11) have such structures as those of Compound Group A shown below.

n in Compound Group A is an arbitrary integer from 0 to 8.

According to the present invention, the orientation control filmrepresented by any of the general formulae (102), (103), (113), (114),(116), (117), (121) and (122) is a copolymer or mixture where thecyclobutane section contains at least one of those represented by thefollowing general formulae (51) through (55).

In the above formulae, each hydrogen molecule of the aromatic ringsindependently may instead be a fluorine atom, chlorine atom, bromineatom, phenyl group, alkyl group containing 1 to 8 carbon atoms, alkoxygroup, vinyl group or alkynyl group. Z is any of the followingfunctional groups, (—CH₂—, —CO₂—, —NH—, —O—, —S—, —SO—, —SO₂—) whereineach hydrogen atom may instead be a fluorine atom, chlorine atom,bromine atom, phenyl group, alkyl group containing 1 to 8 carbon atoms,alkoxy group, vinyl group or alkynyl group.

Since the structure contains the above-mentioned aromatic ring, it ispossible to reduce the resistivity of the alignment film and thereforevery effectively suppress image persistence (burn-in) in liquid crystaldisplay devices.

Note that of the above-mentioned chemical structures, representativeones were employed in orientation control films in the embodimentsdescribed below; however, similar effects are also verified with theother chemical structures.

Embodiments of the present invention will be described below in detailwith reference to the drawings. Hereinafter, a substrate having activeelements such as thin film transistors formed thereon is referred to asan active matrix substrate. Also, the opposite substrate is referred toas a color filter substrate if the substrate is provided with a colorfilter. The present invention is desirably targeted at a contrast ratioof 500:1 or higher. The targeted time within which an image stickingfades away is desirably within 5 minutes. The image sticking fading timeis determined by a method defined in the following embodiments.

Embodiment 1

FIG. 1 schematically depicts a cross-section of one pixel and itsvicinity in the liquid crystal display device of a first embodiment.FIG. 2 schematically depicts the active matrix substrate for explaininghow one pixel is constructed in the liquid crystal display device of thepresent embodiment. FIG. 2A is its top view, FIG. 2B is a cross-sectionalong line A-A′ shown in FIG. 2A, and FIG. 2C is a cross-section alongline B-B′ shown in FIG. 2A. The cross-section shown in FIG. 1corresponds to a part of the cross-section along line A-A′ shown in FIG.2A.

Note that since FIG. 2B and FIG. 2C are depicted schematically withemphasis on the structure of the relevant part, they do not completelyagree with the actual cross-sections along lines A-A′ and B-B′ of FIG.2A. For example, a semiconductor film 116 is not shown in FIG. 2B and,of through holes 118 for connecting common electrodes 103 to a commonline 120, only one is representatively shown in FIG. 2C.

In the present embodiment, a scan line (gate electrode) 104 and thecommon electrode line (common line) 120, which are made of Cr(chromium), are disposed on a glass substrate 101 as the active matrixsubstrate. A gate insulating film 107 of silicon nitride is formed so asto cover the gate electrode 104 and common line 120. On the gateelectrode 104, the semiconductor film 116 of amorphous silicon orpolysilicon is disposed via the gate insulating film 107. Thissemiconductor film 116 serves as the active layer of a thin filmtransistor (TFT) 115 as an active element. In addition, a signal line(drain electrode) 106 and pixel electrode (source electrode) 105, whichare made of Cr.Mo (chromium.molybdenum), are disposed so as to partlyoverlap with the semiconductor film 116 pattern. A protect layer 108 ofsilicon nitride is formed so as to cover all of them.

In FIG. 2C, the common electrode 103 connected to the common line 120 isdisposed on an overcoat layer (organic protect film) 112 via a throughhole 118 formed through the gate insulating film 107 and the protectiveinsulating film 108. In FIG. 2A, a plurality of the common electrodes103 extending from the common line 120 via a plurality of the throughholes 118 are disposed two-dimensionally in the one-pixel region so asto face the pixel electrode 105 of the pixel.

In the present embodiment, pixel electrodes 105 are disposed below theprotective insulating film 108 below the organic protection film 112,and common electrodes 103 are disposed on the organic protection film112. The area sandwiched by these plural pixel electrodes 105 and commonelectrodes 103 constitutes one pixel. In addition, an orientationcontrol film 109 is formed on the top surface of the active matrixsubstrate having a matrix of thus-constructed unit pixels disposedthereon, that is, the orientation control film 109 is formed on theorganic protection film 112 on which the common electrodes 103 areformed.

On the opposite glass substrate 102, a color filter layer 111 isdisposed, as shown in FIG. 1. The color filter 111 is separated for eachpixel by a light blocking film (black matrix) 113. In addition, thecolor filter layer 111 and the light blocking film 113 are covered withan organic protection film 112 of transparent insulating material.Further, an orientation control film 109 is formed on the organicprotection film 112 to constitute the color filter substrate.

To these orientation control films 109, liquid crystal alignment abilityis given by irradiating them with linearly polarized ultraviolet lightobtained from a high-pressure mercury lamp via a pile polarizercomprising a stack of quartz sheets.

The glass substrate 101 constituting the active matrix substrate and theglass substrate 102 constituting the color filter substrate are disposedso as to face each other via the orientation control films 109. Betweenthem, a liquid crystal layer (liquid crystal composition layer) 110′composed of liquid crystals 110 is disposed. In addition, the glasssubstrate 101 constituting the active matrix substrate and the glasssubstrate 102 constituting the color filter substrate have polarizers114 formed respectively on their outer surfaces.

A thin-film-transistor (TFT)-used active matrix liquid crystal displaydevice (TFT liquid crystal display device) is thus constructed. In thisTFT liquid crystal display device, when no electric field is applied,the liquid crystal molecules 110 constituting the liquid crystalcomposition layer 110′ are oriented substantially parallel to themutually facing substrates 101 and 102 and oriented homogeneously in thedirection defined initially by a photo-alignment process.

If the TFT 115 is turned on by applying voltage to the gate electrode104, an electric field 117 is applied to liquid crystal compositionlayer 110′ due to the potential difference between the pixel electrode105 and the common electrodes 103. Accordingly, the orientation of theliquid crystals 110 constituting the liquid crystal composition layer110′ is changed toward the direction of the electric field due to theinteraction between their dielectric anisotropy and the electric field.Utilizing the refractive anisotropy of the liquid crystal layer 110′ andthe polarizers 114 at this time enables changing the transmittance ofthe liquid crystal display device in implementing display.

The organic protection films 112 may be made of acrylic resin superiorin insulation and transparency or thermosetting resin such asepoxy-acrylic resin and polyimide resin. The organic protection films112 may also be made of photo-setting transparent resin or inorganicmaterial such as polysiloxane resin. Further, the organic protectionfilms 112 may be designed to serve as the orientation control films,too.

According to the present embodiment as described so far, it is possibleto give uniform liquid crystal orientation control ability to theorientation control films 109 over the whole display area withoutcausing local disorder of alignment near the electrodes by using thenon-contact photo-alignment technique instead of a buff-used directrubbing alignment technique.

Generally, different from the vertical electric field scheme asrepresented by the conventional TN type, the principle of the IPS typerequires no tilt of the liquid crystal molecules with respect to theboundary faces between the substrates and the liquid crystal layer. Asknown, the smaller the tilt angles of the liquid crystal molecules withrespect to the boundary faces are, the better the viewing anglecharacteristics are. It is therefore preferable and effective if thetilt angles of the liquid crystal molecules are controlled to a smallangle, specifically down to below 1 degree by the orientation controlfilm since the thus-formed liquid crystal display device can remarkablysuppress the color and luminance changes depending on viewing angles.

The following describes how to fabricate the liquid crystal orientationcontrol film of the liquid crystal display device of the presentembodiment by using the rubbingless alignment technique. In the presentembodiment, fabrication of the orientation control film goes through aprocess flow comprising the following steps (1) through (4).

(1) Applying/forming an orientation control film (coating the wholedisplay area with a uniform film)

(2) Imidating the orientation control film by baking (removing thevarnish solvent and promoting the polyimidation for higherthermostability)

(3) Giving liquid crystal alignment ability by irradiating the film withpolarized light (giving uniform alignment ability to the whole displayarea)

(4) Promoting/stabilizing the alignment ability (by heating, infraredirradiation, far-infrared irradiation, electron irradiation, radioactiveirradiation)

The above-mentioned four-step process to fabricate the orientationcontrol film may not be sequentially in the order from (1) to (4).Further effect is expectable in such cases as (a) and (b) below.

(a) Step (4) is temporally overlapped with step (3). Since thisaccelerates the creation of the liquid crystal alignment ability andinduces cross-linking reactions and the like, it is possible to moreeffectively complete the orientation control film.

(b) Step (4) (heating, infrared irradiation, far-infrared irradiation orthe like) is temporally overlapped with steps (2) and (3). Since step(4) also serves to promote the imidation of Step (2), it is possible tomore quickly complete the orientation control film.

The following provides a detailed description of how the liquid crystaldisplay device of the present embodiment is manufactured. As the glasssubstrate 101 constituting the active matrix substrate and as the glasssubstrate 102 constituting the color filter substrate, surface-polished0.7-mm-thick glass substrates are used. The thin film transistor on theglass 101 is constructed from a pixel electrode (source electrode) 105,signal line (drain electrode) 106, scan line (gate electrode) 104 andamorphous silicon 116.

The scan lines 104, common electrode lines 120, signal lines 106 andpixel electrodes 105 were all formed by patterning a chromium film. Thespace between the pixel electrode 105 and the common electrode 103 wasdesigned to be 7 μm. Although the common electrodes 103 and pixelelectrodes 105 used a chromium film due to its low resistivity and easypatterning, it is also possible to use an ITO film in order to formtransparent electrodes and consequently attain higher luminanceperformance.

The gate insulating film 107 and the protective insulating film 108 aremade of silicon nitride and are both 0.3 μm in thickness. After anacrylic resin was applied onto the protective insulating film 108,baking was done at 220 degrees C. for 1 hour, resulting in thetransparent and insulative organic film 112 formed.

Then, a through hole 118 was formed by photolithography and etching. Asshown in FIG. 2C, the through hole 118 was formed down to the commonelectrode line 120. Also, the common electrode 103 connected to thecommon electrode line 120 was formed by patterning.

By the above steps, an active matrix substrate provided thereon with1024×3 (for R, G and B sub-pixels) signal lines 106 and 768 scan lines104 to drive 1024×3×768 pixels was obtained. As shown in FIG. 2A, apixel electrode 105 is disposed among three common electrodes 103 withineach unit pixel (one pixel).

In the present embodiment, the orientation control films 109 were formedfrom a polyamide acid amide represented by the following general formula(101). The prepared varnish is such that its resin content is 5% byweight, DMAc content is 60% by weight, γ-butyrolactone content was is20% by weight, and butylcellosolve content is 15% by weight. After thevarnish was applied to the active matrix substrate by printing, thermalimidation was performed. Consequently, the varnish was imidated by about80%, resulting in an about 70-nm-thick fine orientation control film 109made of polyimide and polyamide acid amide.

Likewise, polyamide acid amide varnish was placed by printing on thesurface of the other glass substrate 102 having an ITO film formedthereon, and the varnish was imidated by about 80%, resulting in anabout 70-nm-thick fine orientation control film 109 made of polyimideand polyamide acid amide. Each orientation control film 109 wasirradiated with polarized UV (ultraviolet) light in order to give theliquid crystal alignment ability to its surface. As the light source, ahigh-pressure mercury lamp was used. UV light in the rage of 240 nm to380 nm was extracted via an interference filter and linearly polarizedat a polarization ratio of about 10:1 through a pile polarizercomprising a stack of quartz sheets. Irradiation energy was given at arate of about 5 J/cm². Consequently, it was found that liquid crystalmolecules on the surface of the orientation control film were orientedperpendicular to the polarization direction of the radiated polarized UVlight.

Then, these two glass substrates 101 and 102 were arranged such thattheir respective orientation control films 109 given the liquid crystalalignment ability faced each other via scattered spacers of globularpolymer beads. By coating their peripheral sections with a sealingagent, they were assembled into a liquid crystal display panel(hereinafter, denoted also as “cell”) of the liquid crystal displaydevice. The liquid crystal alignment directions of the two glasssubstrates are substantially in parallel to each other. Into this cellevacuated, a nematic liquid crystal composition A was injected. Itsdielectric anisotropy Δ∈ is positive, or 10.2 (1 kHz, 20 degrees C.);anisotropic refractive index Δn is 00.75 (wavelength 590 nm, 20 degreesC.); torsional elastic constant K2 is 7.0 pN; and nematic-to-isotropicphase transition temperature T (N-1) is about 76 degrees C. After that,the cell was sealed with UV-curable resin. The liquid crystal layer'sthickness (gap) in the manufactured liquid crystal panel is 4.2 μm.

This liquid display panel has a retardation (ΔN·d) of about 0.31 μm.Preferably, ΔN·d is in the range of 0.2 μm to 0.5 μm. ΔN·d beyond thisrange causes problems such as colored white display. Measuring thepretilt angles of the liquid crystals by a crystal rotation method usinganother homogeneously-aligned liquid crystal display panel which wasconstructed by using substantially the same orientation control film andliquid crystal composition as those used for the above panel revealedthat they were about 0.2 degree. Then, the liquid crystal panel wassandwiched by two polarizers 114 so that the optical transmission axisof one polarizer is substantially parallel to the liquid crystalalignment direction while that of the other is perpendicular to theliquid crystal alignment direction. Then, the liquid crystal displaypanel is connected with the drive circuit, backlight and the like toconstruct a modular active matrix liquid crystal display device. Thepresent embodiment adopted the normally closed switching mechanism inwhich the liquid crystal display device produces dark display at lowvoltage and bright display at high voltage.

Then, the display quality of the liquid crystal display device of thepresent embodiment was evaluated. Its high image quality was verifiedwith a contrast ratio of 500:1; in addition, its wide viewing angle wasverified during its halftone display.

Furthermore, the liquid crystal display device of the present embodimentwas quantitatively evaluated in terms of image burn-in and imagepersistence by using an oscilloscope combined with photodiodes. First, awindow pattern was displayed at the highest luminance on the screen for2 hours. Then, the liquid crystal display device was switched to thehalftone display which made image sticking most noticeable; in thiscase, its was set such that the luminance level became 10% of itsmaximum over the entire screen. The time required for the edges of thewindow pattern to disappear was evaluated as the image sticking fadingtime. The image sticking fading time is required to be within 5 minutes.The measurement results were not longer than 1 minute over the operatingtemperature range (0 to 50 degrees C.). Also by visual image quality andimage sticking check, high display performance was verified. Displayunevenness attributable to image burn-in and image sticking persistencewas not recognized at all.

It is conventionally said that although the photo-alignment can giveliquid crystal alignment ability, the anchoring energy which anchorsaligned liquid crystal molecules to the orientation control film is weakas compared with that obtained by the common rubbing alignment method.It is also said that if this anchoring energy is weak, the reliabilityof the liquid crystal display device as a product is insufficient. Inparticular, in the case of homogenous alignment, it is said that theazimuthal anchoring energy is more important than the polar anchoringenergy.

Then, another liquid crystal cell having an alignment film formed on itsglass substrate was fabricated to measure the strength of the twistcoupling between liquid crystal molecules and the surface of thealignment film at the boundary face, or azimuthal anchoring energy A₂.The alignment film was formed from the same material by using the sameprocess as in the liquid crystal display device described so far. Thealignment film was also given the same alignment treatment. Also, thesame liquid crystal composition as in that liquid crystal display devicewas enclosed therein. The measurement was made by the torque balancemethod (Hasegawa et al, Japanese Liquid Crystal Society ConferenceProceedings 3B12 (2001), p. 251); the result was 8.5×10⁻⁴ N/m.

Comparative Example

As a comparative example to verify the effect of the first embodiment, aliquid crystal display device was constructed. This liquid crystaldisplay device is identical to that of the first embodiment except thata polyamide acid given by the following general formula (111) is used asthe varnish resin to form the 70 nm-thick and about 80% thermallyimidated orientation control films.

Its display quality was evaluated in the same manner as in the firstembodiment. The viewing angle was found substantially as wide as that ofthe first embodiment, and the whole display area exhibited contrastratios beyond 500:1. However, the image sticking fading time measuredquantitatively in the same manner as in the first embodiment was about30 minutes in the operating temperature range of 0 to 50 degrees C. Evenby visual display quality and image sticking check, slow image stickingfading was recognized. The image sticking fading performance was not sohigh as that of the first embodiment. The azimuthal anchoring energy A₂was about 5.5×10⁻⁴ N/m.

Embodiment 2

FIG. 3 schematically depicts a cross-section of one pixel and itsvicinity in the liquid crystal display device of a second embodiment.FIG. 4 schematically depicts the active matrix substrate for explaininghow each pixel is constructed in the liquid crystal display device ofthe second embodiment. FIG. 4A is its top view, FIG. 4B is across-section along line A-A′ shown in FIG. 4A, and FIG. 4C is across-section along line B-B′ shown in FIG. 4A. The cross-section shownin FIG. 3 corresponds to a part of the cross-section along line A-A′shown in FIG. 4A.

Note that since FIG. 4B and FIG. 4C are depicted schematically withemphasis on the structure of the relevant part, they do not completelyagree with the actual cross-sections along lines A-A′ and B-B′ of FIG.4A. For example, the semiconductor film 116 is not shown in FIG. 4B.

In the present embodiment, a gate electrode 104 and common electrodeline 120, which are made of Cr (chromium), are disposed on a glasssubstrate 101 which constitutes the active matrix substrate. A gateinsulating film 107 of silicon nitride is formed so as to cover the gateelectrode 104 and common electrode line 120. On the gate electrode 104,a semiconductor film 116 of amorphous silicon or polysilicon is disposedvia the gate insulating film 107. This semiconductor film 116 serves asthe active layer of a thin film transistor (TFT) 115 as an activeelement.

In addition, a drain electrode 106 and source electrode (pixelelectrode) 105, which are made of chromium.molybdenum, are disposed soas to partly overlap with the semiconductor film 116 pattern. Aprotective insulating film 108 of silicon nitride is formed so as tocover all of them. On this protective insulating film 108, an organicprotect film 112 is disposed. This organic protect film 112 is made of,for example, acrylic resin or other transparent material. The pixelelectrode 105 is made of ITO (In₂O₃:Sn) or other transparent material.The common electrode 103 is connected to the common electrode line 120via a through hole 118 formed through the gate insulating film 107,protect film 108 and organic protect film 112.

The common electrode 103 is formed so as to two-dimensionally surroundone pixel. The common electrode 103 forms a pair with the pixelelectrode 105 in applying an electric field to drive liquid crystals.Also, the common electrode 103 is disposed on the organic protect film112 so that when viewed from the top, it hides the lower drain electrode106, scan line 104, and thin film transistor 115 constituting an activeelement. Thus, the common electrode 103 also serves as a light blockinglayer for the semiconductor film 116.

An orientation control film 109 is formed on the top surface of theglass substrate 101 constituting the active matrix substrate having amatrix of thus-constructed unit pixels disposed thereon. That is, theorientation control film 109 is formed on the organic protect film 112on which the common electrodes 103 are formed. The glass substrate 102constituting the opposite substrate 102 is also provided with anorientation control film 109 on an organic protect film 112 which isformed on a color filter layer 111.

To these orientation control films 109, liquid crystal alignment abilityis given by irradiating them with linearly polarized ultraviolet lightobtained from a high-pressure mercury lamp (a light source) via a pilepolarizer comprising a stack of quartz sheets as in the firstembodiment.

The glass substrate 101 and the opposite glass substrate 102 aredisposed so as to face each other via the orientation control films 109.Between them, a liquid crystal composition layer 110′ composed of liquidcrystals 110 is disposed. In addition, the glass substrate 101 and theopposite glass substrate 102 have polarizers 114 formed respectively ontheir outer surfaces.

Thus, similarly to the first embodiment described earlier, the pixelelectrode 105 is disposed below the organic protect layer 112 andprotective insulating layer 108 while the common electrode 103 isdisposed on the organic protect layer 112 formed over the pixelelectrode 105. The common electrode 103, if its electric resistivity islow enough, may be formed so as to serve both as a common electrode anda common electrode line. In that case, it is possible to omit theformation of the lowermost common electrode line 120 and the associatedprocessing of the through hole 118.

In the present embodiment, as shown in FIG. 4A, each region enclosed bythe lattice-shaped common electrode 103 constitutes one pixel, and thecommon electrode 103 and pixel electrode 105 are disposed so as todivide the pixel into four areas. In addition, the pixel electrode 105and the opposed common electrode 103 forms a zigzag, bent structure withthem disposed parallel to each other, so that one pixel is divided intomultiple sub-pixels. This structure balances out the hue shifts in thepixel.

The following provides a description of how the liquid crystal displaydevice of the second embodiment is manufactured. As the glass substrates101 and 102, surface-polished 0.7-mm-thick glass substrates are used.The thin film transistor 115 is constructed from the pixel electrode(source electrode) 105, signal line (drain electrode) 106, scan line(gate electrode) 104, and amorphous silicon 116. The scan lines 104 wereformed by patterning an aluminum film, the common electrode lines 120and signal lines 106 were formed by patterning a chromium film. Thepixel electrodes 105 were formed by patterning an ITO film. Except thescan lines 104, the electrode line patterns are bent zigzag by 10degrees as shown in FIG. 4A. The gate insulating film 107 and theprotective insulating film 108 are made of silicon nitride and both 0.3μm in thickness.

Then, as shown in FIG. 4C, each cylindrical through hole 118 with adiameter of about 10 μm was formed down to the common electrode line 120by a photolithography technique and etching process, and acrylic resinwas applied thereon. An about 1-μm-thick organic protect film 112 with adielectric constant of about 4 was formed as a transparent, insulativefilm by heating it for 1 hour at 220 degrees C. This organic protectfilm 112 planarizes the surface irregularities caused by the step of thepixel electrode 105 in the display region. Likewise, the other organicprotect film 112 planarizes the surface irregularities of the boundaryface of the color filter layer 111 between adjacent pixels.

Then, after the through hole 118 was re-etched to a diameter of about 7μm, the common electrode 103 was formed thereon by patterning an ITOfilm for connection with the common electrode line 120. The spacebetween the pixel electrode 105 and the common electrode 103 was 7 μm.Further, this common electrode 103 was arranged in such a lattice formthat it enclosed the pixel by covering the lower signal line 106, scanline 104 and thin film transistor 115. Thus, the common electrode 103serves also as a light blocking layer.

Accordingly, the pixel electrode 105 was arranged along the three barsof the common electrode 103 in the unit pixel as shown in FIG. 4A.Consequently, an active matrix substrate was obtained on which1024×3×768 pixels were constructed from 1024×3 (for R, G and Bsub-pixels) signal lines 106 and 768 scan lines 104.

In the present embodiment, the orientation control films 109 were formedfrom a polyamide acid trimethyl silyl ester varnish given by thefollowing general formula (112). The prepared varnish is such that itsresin content is 5% by weight, DMAc content is 60% by weight,γ-butyrolactone content is 20% by weight, and butylcellosolve content is15% by weight. After the varnish was applied to the active matrixsubstrate by printing, thermal imidation was performed. Consequently,the varnish was imidated by about 80%, resulting in an about 60-nm-thickfine orientation control film 109 made of polyimide and polyamide acidalkyl silyl ester.

The process to impart alignment ability was similar to that for thefirst embodiment. The orientation control films ware irradiated withpolarized ultraviolet light at an irradiation energy of about 3 J/cm².Also, thermal treatment was concurrently performed on the substrate atabout 150 degrees C. by setting it on a hot plate while the orientationcontrol film formed on the substrate was irradiated with polarized UVlight.

Then, these two glass substrates were arranged so that the respectiveorientation control films 109 given the liquid crystal alignment abilityfaced each other via scattered spacers of globular polymer beads. Bycoating their peripheral sections with a sealing agent, they wereassembled into a liquid crystal display panel. The liquid crystalalignment directions of the two glass substrates are substantially inparallel to each other.

Into this liquid crystal display panel evacuated, the nematic liquidcrystal composition A was injected. Its dielectric anisotropy Δ∈ is apositive value of 10.2 (1 kHz, 20 degrees C.); anisotropic refractiveindex Δn is 0.075 (wavelength 590 nm, 20 degrees C.); torsional elasticconstant K is 7.0 pN; and nematic-to-isotropic phase transitiontemperature T (N-1) is about 76 degrees C. After that, the panel wassealed with UV-curable resin. The liquid crystal layer's thickness (gap)is 4.2 μm. The retardation (Δnd) of this liquid display panel is about0.31 μm.

Measuring the pretilt angles of the liquid crystals by the crystalrotation method using another homogeneously-aligned liquid crystaldisplay panel which was constructed by using substantially the sameorientation control film and liquid crystal composition as those usedfor the above panel revealed that they were about 0.2 degrees. Then, theliquid crystal panel was sandwiched by two polarizers 114 such that theoptical transmission axis of one polarizer was substantially parallel tothe liquid crystal orientation direction while that of the other wasorthogonal to the liquid crystal orientation direction. Then, the liquidcrystal display panel was connected with a drive circuit, backlight, andthe like to construct a modular active matrix liquid crystal displaydevice. The present embodiment employed the normally closed switchingmechanism in which dark display is provided at low voltage, and brightdisplay is provided at high voltage.

Then, the display quality of the liquid crystal display device of thepresent embodiment was evaluated. The liquid crystal display device wasverified to have a higher aperture ratio and a higher contrast ratio(600:1) than those of the first embodiment. Its wide viewing angle wasalso verified during its halftone display. In addition, this liquidcrystal display device was quantitatively evaluated in terms of theimage sticking fading time in the same manner as in the firstembodiment. The image sticking fading time was measured to be about 1minute in the operating temperature range from 0 to 5 degrees C. Also byvisual image quality and image sticking check, display unevennessattributable to image burn-in and image sticking persistence was notrecognized at all. The display performance was as high as that of thefirst embodiment.

Embodiment 3

FIG. 5 schematically depicts a cross-section of one pixel and itsvicinity in the liquid crystal display device of a third embodiment.Note that in the drawing, the same reference numerals as those of theprevious embodiments denote functionally identical parts. In the presentembodiment as shown in FIG. 5, the pixel electrode 105 disposed belowthe protective insulating film 108 is extended upward across the organicprotect film 112 via a through hole 118 to the same level as the commonelectrode 103. In the case of this construction, it is possible tofurther lower the liquid crystal drive voltage.

In the TFT liquid crystal display device as constructed above, when noelectric field is applied, the liquid crystal molecules 110 constitutingthe liquid crystal composition layer 110′ are substantially parallel tothe mutually facing substrates 101 and 102 and oriented homogeneously inthe direction defined initially by the photo-alignment process. If theTFT 115 is turned on by applying voltage to the gate electrode 104, anelectric field 117 is applied to the liquid crystal composition layer110′ due to the potential difference between the pixel electrode 105 andthe common electrodes 103. Accordingly, the orientation of the liquidcrystals 110 is changed toward the direction of the electric field dueto the interaction between the dielectric anisotropy of the liquidcrystals and the electric field. Utilizing the refractive anisotropy ofthe liquid crystal layer 110′ and the polarizers 114 at this timeenables changing the transmittance of the liquid crystal display devicein implementing display.

The following provides a description of how the liquid crystal displaydevice of the third embodiment is manufactured. As the glass substrates101 and 102, surface-polished 0.7-mm-thick glass substrates are used.The thin film transistor 115 is constructed from the pixel electrode(source electrode) 105, signal line (drain electrode) 106, scan line(gate electrode) 104, and amorphous silicon 116. The scan electrodes 104are formed by patterning an aluminum film. The common electrode lines120, signal lines 106, and pixel electrodes 105 are formed by patterninga chromium film. The gate insulating film 107 and the protectiveinsulating film 108 are made of silicon nitride and both 0.3 μm inthickness. After acrylic resin is applied thereon, thermal treatment isdone at 220 degrees C. for 1 hour to form an about 1.0-μm-thick,transparent, insulative organic protect film 112 with a dielectricconstant of about 4. This organic protect film 112 planarizes thesurface irregularities caused by the step of the pixel electrode 105 inthe display region and those between adjacent pixels.

Then, the cylindrical through hole 118 with a diameter of about 10 μm isformed down to the lower source electrode 105 by a photolithographytechnique and etching process as shown in FIG. 5. By patterning an ITOfilm, the pixel electrode 105 is then formed thereon for connection withthe source electrode 105. In addition, an about 10-μm-wide cylindricalthough hole is formed on the common electrode line 120. The commonelectrode 103 is formed thereon by patterning an ITO film. There is aspace of 7 μm between the pixel electrode 105 and the common electrode103. Except the scan lines 104, the electrode line patterns are bentzigzag by 10 degrees. Further, this common electrode 103 is arranged insuch a lattice form that it encloses the pixel by covering the lowersignal line 106, scan line 104, and thin film transistor 115. Thus, thecommon electrode 103 serves also as a light blocking layer.

Accordingly, similarly to the second embodiment except that two kinds ofthrough holes are formed in the unit pixel, the pixel electrode 105 isarranged along the three bars of the common electrode 103. Consequently,an active matrix substrate is obtained on which 1024×3×768 pixels areconstructed from 1024×3 (for R, G and B sub-pixels) signal lines 106 and768 scan lines 104.

As shown in FIG. 5, except for the pixel structure and the orientationcontrol films, the liquid crystal display device of the presentembodiment is the same as that of the second embodiment. In the presentembodiment, the orientation control films 109 are formed from apolyamide acid ester varnish given by the following general formula(115). The prepared varnish is such that its resin content is 5% byweight, DMAc content is 60% by weight, γ-butyrolactone content is 20% byweight, and butylcellosolve content is 15% by weight. After the varnishis applied to the substrate by printing, thermal imidation is performed.The varnish is imidated by about 80%, resulting in the formation of anabout 80-nm-thick fine orientation control film 109 made of polyimideand polyamide acid ester.

The process to impart alignment ability is similar to that for the firstembodiment. The alignment films are irradiated with polarizedultraviolet light at an energy rate of about 6 J/cm². Also, thermaltreatment is concurrently performed at about 180 degrees C. on thesubstrate by setting it on a hot plate while the orientation controlfilm formed on the substrate is irradiated with polarized UV light.

The display quality of the liquid crystal display device of the presentembodiment was evaluated. Its display quality was as high as that of thefirst embodiment. Its wide viewing angle was also verified during itshalftone display. In addition, this liquid crystal display device wasquantitatively evaluated in terms of the image sticking fading time inthe same manner as in the first embodiment. The image sticking fadingtime was measured to be about 1 minute or shorter. Also by visual imagequality and image sticking check, high display performance wasrecognized; specifically, display unevenness attributable to imageburn-in and image sticking persistence was not recognized at all.

If the pixel electrode 105 connected directly with the TFT 115 is incontact with the orientation control film 109 formed on the top of thesubstrate as shown in FIG. 5, ordinary rubbing alignment treatment maydamage the TFT 115 which is subject to frictionally charged electricityvia the pixel electrode near the surface. In the case of such anarrangement, rubbingless photo-alignment treatment, as in the presentembodiment, is very effective.

Embodiment 4

FIG. 6 schematically depicts a cross-section of one pixel and itsvicinity in the liquid crystal display device of a fourth embodiment. Inthe drawing, the same reference numerals as those of the previousembodiments denote functionally identical parts. The structure of thepresent embodiment has large steps due to electrodes and the like. Asshown in FIG. 6, the gate electrode 104 of the thin film transistor 115and the common electrode 103 are formed in the same layer. Theorientation of the liquid crystals 110 is changed toward the electricfield 117 between the common electrode 103 and the pixel electrode 105.

Note that each embodiment mentioned so far may be configured to have aplurality of display regions per pixel by forming a common electrode 103and a pixel electrode 105 for each display region. If plural sets arethus formed, it is possible to shorten the pixel electrode 105 to commonelectrode 103 distance. Therefore, this structure is very effective inlowering the liquid crystal drive voltage when each pixel is large.

Also note that, in light of fabrication easiness and reliability, it isnot necessary but preferable in each embodiment described so far to useion-doped titanium oxide or ion-doped zinc oxide as in ITO (indium tinoxide) as the material of a transparent conductive film whichconstitutes the pixel electrodes and/or common electrodes.

In the manufacture method of the liquid crystal display device of thefourth embodiment, surface-polished 0.7-mm-thick glass substrates areused as the glass substrates 101 and 102. The thin film transistor 115is constructed from the pixel electrode (source electrode) 105, signalline (drain electrode) 106, scan line (gate electrode) 104, andamorphous silicon 116. The scan electrode 104, common electrode line120, signal line 106, pixel electrode 105, and common electrode 103 areall formed by patterning a chromium film. The pixel electrode 105 tocommon electrode 103 space is 7 μm. The gate insulating film 107 and theprotective insulating film 108 are made of silicon nitride and both 0.3μm in thickness.

In the present embodiment, the orientation control films 109 are formedfrom a mixed resin containing a polyamide acid ester given by thefollowing general formula (118) and a polyamide acid given by thefollowing general formula (119) at a weight ratio of 7:3. The preparedmixed resin is such that its resin content is 5% by weight, DMAc contentis 60% by weight, γ-butyrolactone content is 20% by weight, andbutylcellosolve content is 15% by weight. After the mixed resin isapplied to the substrate by printing, thermal imidation is performed.The mixture was imidated by about 80%, resulting in the formation of anabout 100-nm-thick fine orientation control film 109 made of polyimideand polyamide ester.

The measured resistivity of this orientation control film was 1.5×10¹⁵Ωcm.

Then, the orientation control film is given photo-alignment treatment.Specifically, the film is irradiated with polarized UV light having 220to 380 nm wavelengths at an irradiation energy rate of about 3 J/cm²while irradiated concurrently with infrared light. The polarized UVlight is obtained from a high-pressure mercury lamp via an interferencefilter and a pile polarizer comprising a stack of quartz sheets. Bythis, an active matrix substrate provided thereon with 1024×3 (for R, Gand B sub-pixels) signal lines 106 and 768 scan lines 104 to drive1024×3×768 pixels is completed.

The liquid crystal display device of the present embodiment constructedas describe above, shown in FIG. 6, is the same as that of the firstembodiment except for the pixel structure.

The display quality of the liquid crystal display device of the presentembodiment was evaluated. Its display quality was as high as that of thefirst embodiment. Its wide viewing angle was also verified during itshalftone display. In addition, this liquid crystal display device wasquantitatively evaluated in terms of the image sticking fading time inthe same manner as in the first embodiment. The image sticking fadingtime was below 3 minutes. Also by visual image quality and imagesticking check, defective display attributable to image burn-in andimage sticking persistence was not recognized.

In addition, another liquid crystal display device was constructed. Thisliquid crystal display device is the same as that of the former exampleexcept that only the polyamide acid ester given by the following generalformula (118) is used as the varnish resin for the orientation controlfilm.

The measured resistivity of this orientation control film was 6.0×10¹⁵Ωcm.

The display quality of this example was evaluated. The display qualitywas as high as that of the former example. Its wide viewing angle wasalso verified during its halftone display. Then, this sample wasquantitatively evaluated in terms of the image sticking fading time inthe same manner as in the former example. The image sticking fading timewas 5 minutes or shorter, which is somewhat longer than that of theformer example. However we confirmed this sample provides enoughperformance for the problems to be resolved by this invention.

Embodiment 5

FIG. 7 schematically depicts a cross-section of one pixel and itsvicinity in the liquid crystal display device of a fifth embodiment. Inthe drawing, the same reference numerals as those of the previousembodiments denote functionally identical parts. In the presentembodiment, the pixel electrode 105 and common electrode 103 are made ofITO. The common electrode 103 is designed to be so flat and wide as tooccupy substantially the whole area of the pixel. This construction canraise the aperture ratio since the portion above the electrode can beutilized as a light-transmissive portion. In addition, it is possible toeffectively apply an electric field since the inter-electrode space canbe shortened.

FIG. 8 schematically depicts an active matrix substrate of the presentembodiment for explaining how a thin film transistor 115, commonelectrode 103, pixel electrode 105, and signal line 106 are structuredto construct one pixel.

In the manufacture method of the liquid crystal display device of thepresent embodiment, a surface-polished 0.7-mm-thick glass substrate isused as the glass substrates 101. The glass substrate 101 is formed intoa TFT substrate on which are formed common electrodes 103, pixelelectrodes 105, signal lines 106, scan lines 104, a gate insulating film107 to prevent short-circuits between the signal lines 106 and the scanlines 104, thin film transistors 115, pixel electrodes 105, signal lines106, and a protective insulating film 108 to protect the pixelelectrodes 105 and signal lines 106.

The TFT 115 is constructed from the pixel electrode (source electrode)105, signal line (drain electrode) 106, scan line (gate electrode) 104,and amorphous silicon 116. The scan line (gate electrode) 104 is formedby pattering an aluminum film; the signal line (drain electrode) 106formed by pattering a chromium film; and the common electrode 103 andpixel electrode 105 formed by pattering ITO.

The gate insulating film 107 and the protective insulating film 108 aremade of silicon nitride and are 0.2 μm and 0.3 μm in thickness,respectively. Capacitive elements are formed by sandwiching the gateinsulating film 107 and protective insulating film 108 between the pixelelectrode 105 and common electrode 103.

The pixel electrode 105 is disposed on an upper-layer of the flat commonelectrode 103. 1024×3×768 pixels are constructed from 1024×3 (for R, Gand B sub-pixels) signal lines 106 and 768 scan lines 104.

The substrate 102 is the opposite color filter substrate on which acolor filter 113 provided with a black matrix 113 is formed as in thefirst embodiment.

Then, the orientation control films 109 are formed from a resincontaining a polyamide acid ester given by the following general formula(120). The prepared resin is such that its resin content is 5% byweight, DMAc content is 60% by weight, γ-butyrolactone content is 20% byweight, and butylcellosolve content is 15% by weight. After the resin isapplied to the substrate by printing, thermal imidation is performed.The resin is imidated by about 80%, resulting in an about 110-nm-thickfine orientation control film 109 made of polyimide and polyamide acidester.

The measured resistivity of this orientation control film was 4.5×10¹⁵Ωcm.

Likewise, the same polyamide acid ester varnish is printed on thesurface of the other glass substrate 102 having an ITO film formedthereon, and the varnish is thermally imidated by about 80%, resultingin an about 110-nm-thick fine orientation control film 109 made ofpolyimide and polyamide acid ester.

In order to impart liquid crystal alignment ability to the surface ofeach orientation control film 109, the films were irradiated withpolarized UV (ultraviolet) light together with infrared light. As thelight source, a high-pressure mercury lamp was used. The UV light in therange of 240 nm to 380 nm was extracted and linearly polarized to apolarization ratio of about 10:1 through a pile polarizer comprising astack of quartz sheets. Irradiation energy was given at a rate of about2.5 J/cm². The temperature of each orientation control film was about180 degrees C. during the irradiation. Consequently, it was found thatliquid crystal molecules on the surfaces of the orientation controlfilms were oriented orthogonal to the polarization direction of theradiated UV light.

The liquid crystal alignment directions of the orientation control films109 of the TFT and color filter substrates were parallel to each other.With polymer-bead spacers with an average grain size of 4 μm scatteredbetween the TFT substrate and the color filter substrate, liquid crystalmolecules 110 were injected between these two glass substrates. As theliquid crystals 110, the same liquid crystal composition A as in thefirst embodiment was used.

Two polarizers 114 which sandwich the TFT substrate and color filtersubstrate are set in a crossed-Nicol state. The normally closedswitching mechanism is employed in which dark display is provided at lowvoltage, and bright display is provided at high voltage.

Then, the display quality of the liquid crystal display device of thepresent embodiment was evaluated. Its image quality was verified to havea higher aperture ratio and a higher contrast ratio of 700:1 than thoseof the first embodiment. Its wide viewing angle was also verified duringits halftone display. In addition, this liquid crystal display devicewas quantitatively evaluated in terms of the image sticking fading timein the same manner as in the first embodiment. The image sticking fadingtime was about 5 minutes in the operating temperature range of 0 to 50degrees C. Also by visual image quality and image sticking check,display unevenness attributable to image burn-in and image persistencewas not recognized at all. The display performance was as high as thatof the first embodiment.

Embodiment 6

The liquid crystal display device of a sixth embodiment is the same asthat of the fifth embodiment except that the orientation control film109 is formed from a copolymer varnish which is a polymer chain given bythe following general formula (120) including about 20% of a polyamideacid ester given by the general formula (125).

The measured resistivity of this orientation control film was 5.2×10¹⁴Ωcm.

Then, the display quality of the liquid crystal display device of thepresent embodiment was evaluated. Its high image quality was verifiedwith a high contrast ratio of 690:1. Its wide viewing angle was alsoverified during its halftone display. In addition, this liquid crystaldisplay device was quantitatively evaluated in terms of the imagesticking fading time in the same manner as in the first embodiment. Theimage sticking fading time was 3 minutes in the operating temperaturerange of 0 to 50 degrees C. Also by visual image quality and imagesticking check, display unevenness attributable to image burn-in andimage persistence was not recognized at all. The display performance wasvery high.

Embodiment 7

The liquid crystal display device of a seventh embodiment is the same asthat of the fifth embodiment except that the orientation control film109 is formed from a polyamide acid ester varnish given by the followinggeneral formula (123).

The measured resistivity of this orientation control film was 5.7×10¹⁵Ωcm.

Then, the display quality of the liquid crystal display device of thepresent embodiment was evaluated. Its high image quality was verifiedwith a high contrast ratio of 730:1. Its wide viewing angle was alsoverified during its halftone display. In addition, this liquid crystaldisplay device was quantitatively evaluated in terms of the imagesticking fading time in the same manner as in the first embodiment. Theimage sticking fading time was 5 minutes in the operating temperaturerange of 0 to 50 degrees C. Also by visual image quality and imagesticking check, display unevenness attributable to image burn-in andimage persistence was not recognized at all. The display performance wasvery high.

Embodiment 8

The liquid crystal display device of an eighth embodiment is the same asthat of the fifth embodiment except that the orientation control film109 is formed from a mixed varnish containing polyamide acid estersgiven respectively by the following general formulae (123) and (124) ata weight ratio of 7:3.

The measured resistivity of this orientation control film was 2.5×10¹⁴Ωcm.

Then, the display quality of the liquid crystal display device of thisembodiment was evaluated. Its high image quality was verified with ahigh contrast ratio of 710:1. Its wide viewing angle was also verifiedduring its halftone display. In addition, this liquid crystal displaydevice was quantitatively evaluated in terms of the image stickingfading time in the same manner as in the first embodiment. The imagesticking fading time was 3 minutes in the operating temperature range of0 to 50 degrees C. Also by visual image quality and image stickingcheck, display unevenness attributable to image burn-in and imagepersistence was not recognized at all. The display performance was veryhigh.

Embodiment 9

The liquid crystal display device of a ninth embodiment is the same asthat of the first embodiment except that the orientation control film109 is formed from a copolymer varnish which is a polymer chain given bythe following general formula (120) including about 15% of a polyamideacid ester given by the general formula (126).

The measured resistivity of this orientation control film was 7.1×10¹⁴Ωcm.

Then, the display quality of the liquid crystal display device of thepresent embodiment was evaluated. Its high image quality was verifiedwith a high contrast ratio of 730:1. Its wide viewing angle was alsoverified during its halftone display. In addition, this liquid crystaldisplay device was quantitatively evaluated in terms of the imagesticking fading time in the same manner as in the first embodiment. Theimage sticking fading time was 3 minutes in the operating temperaturerange of 0 to 50 degrees C. Also by visual image quality and imagesticking check, display unevenness attributable to image burn-in andimage persistence was not recognized at all. The display performance wasvery high.

What is claimed is:
 1. A liquid crystal display device comprising: a pair of substrates, at least one of which is transparent; a liquid crystal layer disposed between the pair of substrates; a group of electrodes formed on at least one of the pair of substrates to apply an electric field to the liquid crystal layer; plural active elements connected to the group of electrodes; and a liquid-crystal orientation control film disposed on at least one of the pair of substrates; wherein said orientation control film is made of a photosensitive polyimide, a polyamide acid ester and a polyamide acid, and is given orientation control ability by being irradiated with substantially linearly polarized light; wherein the pretilt angles of the liquid crystal molecules of the liquid crystal layer are not larger than 1 degree; wherein the polyamide acid ester contains a polyamide acid ester that contains a polymer unit given by the following formula (116) and/or (117), or a polyamide acid ester that contains a polymer unit given by the following formula (116) and/or (117) and a polymer unit given by the following formula (116) and/or (117) wherein the cyclobutane section is replaced with a section given by at least one of the following general formulae (51) through (55):

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound; wherein the photosensitive polyimide comprises polyimide formed by imidating a polyamide acid ester that contains a polymer unit given by the above formula (116) and/or (117), or a polyamide acid ester that contains a polymer unit given by the above formula (116) and/or (117) and a polymer unit given by the above formula (116) and/or (117) wherein the cyclobutane section is replaced with a section given by at least one of the following general formulae (51) through (55); wherein the polyamide acid contains a polyamide acid that contains a polymer unit given by the following formula (121) and/or (122), or a polyamide acid that contains a polymer unit given by the following formula (121) and/or (122) and a polymer unit given by the following formula (121) and/or (122) wherein the cyclobutane section is replaced with a section given by at least one of the following general formulae (51) through (55):

wherein each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound,

wherein each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), and wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 2. The liquid crystal display device according to claim 1, wherein the aromatic compound Ar contains at least one of those given by the following general formulae (1) through (11)

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; X is an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, an vinyl group, an alkynyl group, or an alkyl group containing 0 to 8 carbon atoms and any of the following functional groups, (—O—, —CO—, —COO—, —S—, —SO—, —SO2-, —NH—, —N═N—, phenyl group); Y is an aromatic ring such as a phenyl group, a naphthyl group, an anthracene group, or a pyrene group wherein each hydrogen atom of the aromatic ring individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group.
 3. The liquid crystal display device according claim 1 wherein the electric field applied to the liquid crystal layer has a component which is substantially parallel to the surface of a substrate on which the group of electrodes is formed.
 4. The liquid crystal display device according claim 1 wherein the longitudinal direction of liquid crystals constituting the liquid crystal layer on the orientation control film is parallel or orthogonal to the polarization axis of the substantially linearly polarized light.
 5. The liquid crystal display device according claim 1 wherein the retardation Δn·d of the liquid crystal layer satisfies the condition of 0.2 μm≦Δn·d≦0.5 μm where Δn and d respectively represent the refractive anisotropy and thickness of the liquid crystal layer.
 6. The liquid crystal display device according claim 1 wherein the dielectric anisotropy Δ∈ of the liquid crystal molecules in the liquid crystal layer is positive.
 7. The liquid crystal display device according to claim 1 wherein the polyamide acid ester further contains a polymer unit given by the general formula (116) or (117) wherein the cyclobutane section is replaced with at least one section given by the following general formulae (51) through (55) or wherein the orientation control film further contains a polyamide acid ester that contains a polymer unit given by the general formula (116) or (117) wherein the cyclobutane section is replaced with at least one section given by the following general formulae (51) through (55) or the polyamide acid that further contains a polymer unit given by the general formula (121) or (122), wherein the cyclobutane section is replaced with at least one section given by the following general formulae (51) through (55)

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 8. The liquid crystal display device according to claim 1 wherein one or more of R2 is CH₃.
 9. The liquid crystal display device according to claim 1 wherein R2 at the 1-position is CH₃ and R2 at the 3-position is CH₃.
 10. The liquid crystal display device according to claim 1 wherein the polyamide acid ester contains the polymer unit given by the following formula (116).
 11. The liquid crystal display device according to claim 10, wherein the orientation control film further contains a polyamide acid that contains a polymer unit given by the following formula (121)

wherein each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-CH≡CH, m=0, 1, 2), and Ar is an aromatic compound.
 12. The liquid crystal display device according to claim 10, wherein the orientation control film further contains a polyamide acid that contains a polymer unit given by the following formula (122)

wherein each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound.
 13. The liquid crystal display device according to claim 10, wherein the orientation control film further contains a polyamide acid that contains a polymer unit given by the following formula (121) wherein the cyclobutane section is replaced with a section given by at least one of the following general formulae (51) through (55)

wherein each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound,

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 14. The liquid crystal display device according to claim 10, wherein the orientation control film further contains a polyamide acid that contains a polymer unit given by the following formula (122) wherein the cyclobutane section is replaced with a section given by at least one of the following general formulae (51) through (55)

wherein each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound,

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 15. The liquid crystal display device according to claim 1, wherein the polyamide acid ester contains a polymer unit given by the following formula (117)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and further contains a polyamide acid that contains a polymer unit given by the following formula (122)

wherein each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound.
 16. The liquid crystal display device according to claim 1, wherein the polyamide acid ester contains a polymer unit given by the following formula (117)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and further contains a polyamide acid that contains a polymer unit given by the following formula (121) wherein the cyclobutane section is replaced with a section given by at least one of the following general formulae (51) through (55)

wherein each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound,

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 17. The liquid crystal display device according to claim 1, wherein the polyamide acid ester contains a polymer unit given by the following formula (117)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and further contains a polyamide acid that contains a polymer unit given by the following formula (122) wherein the cyclobutane section is replaced with a section given by at least one of the following general formulae (51) through (55)

wherein each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound,

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 18. The liquid crystal display device according to claim 1, wherein the aromatic compound Ar contains at least one of those given by the following general formulae (1) through (6) and (9) through (11)

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; X is an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, an vinyl group, an alkynyl group, or an alkyl group containing 0 to 8 carbon atoms and any of the following functional groups, (—O—, —CO—, —COO—, —S—, —SO—, —SO2-, —NH—, —N═N—, phenyl group); Y is an aromatic ring such as a phenyl group, a naphthyl group, an anthracene group, or a pyrene group wherein each hydrogen atom of the aromatic ring individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group.
 19. The liquid crystal display device according to claim 1, wherein the aromatic compound Ar contains at least one of those given by the following general formulae (7) and (8)

wherein: X is an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, an vinyl group, an alkynyl group, or an alkyl group containing 0 to 8 carbon atoms and any of the following functional groups, (—O—, —CO—, —COO—, —S—, —SO—, —SO2-, —NH—, —N═N—, phenyl group); and Y is an aromatic ring such as a phenyl group, a naphthyl group, an anthracene group, or a pyrene group wherein each hydrogen atom of the aromatic ring individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group.
 20. The liquid crystal display device according to claim 1, wherein the polyamide acid ester is a copolymer that contains a polymer unit given by the following formula (116)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and a polymer unit given by the general formula (116) wherein the cyclobutane section is replaced with at least one section given by the following general formulae (51) through (55)

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 21. The liquid crystal display device according to claim 1, wherein the polyamide acid ester is a copolymer that contains a polymer unit given by the following formula (116)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and a polymer unit given by the following general formula (117)

wherein the cyclobutane section is replaced with at least one section given by the following general formulae (51) through (55)

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 22. The liquid crystal display device according to claim 1, wherein the polyamide acid ester is a copolymer that contains a polymer unit given by the following formula (117)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and a polymer unit given by the general formula (116)

wherein the cyclobutane section is replaced with at least one section given by the following general formulae (51) through (55)

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 23. The liquid crystal display device according to claim 1, wherein the polyamide acid ester is a copolymer that contains a polymer unit given by the following formula (117)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and a polymer unit given by the general formula (117) wherein the cyclobutane section is replaced with at least one section given by the following general formulae (52) through (55)

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 24. The liquid crystal display device according to claim 1, wherein the polyamide acid ester contains a polymer unit given by the following formula (116)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and further contains a polyamide acid ester that contains a polymer unit given by the general formula (116) wherein the cyclobutane section is replaced with at least one section given by the following general formulae (51) through (55)

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 25. The liquid crystal display device according to claim 1, wherein the polyamide acid ester contains a polymer unit given by the following formula (116)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and further contains a polyamide acid ester that contains a polymer unit given by the following general formula (117)

wherein the cyclobutane section is replaced with at least one section given by the following general formulae (51) through (55)

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 26. The liquid crystal display device according to claim 1, wherein the polyamide acid ester contains a polymer unit given by the following formula (117)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and further contains a polyamide acid ester that contains a polymer unit given by the following general formula (116)

wherein the cyclobutane section is replaced with at least one section given by the following general formulae (51) through (55)

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 27. The liquid crystal display device according to claim 1, wherein the polyamide acid ester contains a polymer unit given by the following formula (117)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and further contains a polyamide acid ester that contains a polymer unit given by the general formula (117) wherein the cyclobutane section is replaced with at least one section given by the following general formulae (51) through (55)

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 28. The liquid crystal display device according to claim 1, wherein the polyamide acid ester contains a polymer unit given by the following formula (116)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and further contains polyamide acid that contains a polymer unit given by the following formula (121) wherein the cyclobutane section is replaced with a section given by at least one of the following general formulae (51) through (55)

wherein each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound,

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 29. The liquid crystal display device according to claim 1, wherein the polyamide acid ester contains a polymer unit given by the following formula (116)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and further contains polyamide acid that contains a polymer unit given by the following formula (122) wherein the cyclobutane section is replaced with a section given by at least one of the following general formulae (51) through (55)

wherein each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound,

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 30. The liquid crystal display device according to claim 1, wherein the polyamide acid ester contains a polymer unit given by the following formula (117)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and further contains polyamide acid that contains a polymer unit given by the following formula (121) wherein the cyclobutane section is replaced with a section given by at least one of the following general formulae (51) through (55)

wherein each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound,

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group.
 31. The liquid crystal display device according to claim 1, wherein the polyamide acid ester contains a polymer unit given by the following formula (117)

wherein each R1 is individually an alkyl group containing 1 to 8 carbon atoms, each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound, and further contains polyamide acid that contains a polymer unit given by the following formula (122) wherein the cyclobutane section is replaced with a section given by at least one of the following general formulae (51) through (55)

wherein each R2 is individually a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, a vinyl group (—(CH2)m-CH═CH2, m=0, 1, 2), or an alkynyl group (—(CH2)m-C≡CH, m=0, 1, 2), and Ar is an aromatic compound,

wherein: each hydrogen molecule of the aromatic rings individually may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group, or an alkynyl group; and Z is any of the following functional groups, (—CH2-, —CO2-, —NH—, —O—, —S—, —SO—, —SO2-), wherein each hydrogen atom may instead be a fluorine atom, a chlorine atom, a bromine atom, a phenyl group, an alkyl group containing 1 to 8 carbon atoms, an alkoxy group, a vinyl group or an alkynyl group. 